My 15 month old wants to eat nothing but bread?

My daughter is 15 1/2 months old and up until a few weeks ago was a great eater. She wasn't picky and ate good sized portions. However, since about the middle of May she refuses anything I try to feed her, including foods that were previous favorites (yogurt, mac & cheese, etc.) She eats a bite or two and that's it. Instead she brings me the loaf of bread (no matter how where I put it that I think it's out of reach) and cries until I give her a piece. She easily eats 4 slices a day, sometimes back-to-back. She's also started drinking between 50-60oz. a day which is almost double what she was before. I've tried feeding her before she gets her cup but she refuses the food every time until she gets her cup. I did talk to her pediatrician when this first started and he said it's normal for a toddler's appetite to go down until about the age of 2 but is this more extreme than he was talking about? If so, how do I get my healthy eater back??? And should I be concerned???? (More than I am, obviously.)